1. Field of Invention
This invention pertains to an apparatus for automatic measure of the volume and flow rate of air exhaled by a person, and more particularly, to a personal spirometer small enough so that it can be carried unobtrusively in a pocket so that person can use it easily with maximum convenience and minimum embarrassment.
2. Description of the Prior Art
Spirometers are devices used to measure the volume and flow rate of air exhaled by a person. These measurements are important of general physiological studies and for diagnostic analysis of particular patients. For example, the effects of various medicines used to treat patients with pulmonary or asthmatic problems can be best analyzed by monitoring the volume and flow rate of air exhaled at regular intervals before and after the administration of medication.
In general, spirometers make their measurement by one of two means. One type collects the exhaled volume from the subject into a bellows or other container, the displacement of which corresponds to the volume of exhaled air. These devices are by their nature large to allow sufficient air collection volume and hence are not easily made portable. A second type measures the rate of air flow through a flow measurement device. Exhaled volume is derived by integration of the air flow rate over some period of time.
Until the present invention, spirometers were rather bulky and expensive devices found mostly in clinics and laboratories. Their operation required a trained technician. Furthermore, most such devices were complicated so that they could not be made small enough to be carried in a pocket. For example, there are several devices available in the market known as pneumotachs, such as the Fleisch Pneumotach. These devices depend on a laminar air flow past a resistance element. Such devices need additional means for insuring that the flow remains laminar even at high air velocities. Therefore, these type of devices are inherently complex and relatively large. Furthermore the resistance element frequently includes a screen disposed directly in the air path. This screen intercepts impurities which clog the screen and change the response of the device and in addition are unsanitary. The pneumotach also includes pressure measurement ports which frequently become occluded from moisture or impurities, thus adversely altering the accuracy of measurement.